This study is designed to explore the genetics of familial cerebral aneurysms. Families in which more than one person has had a known cerebral aneurysm will be studied. Family histories will be obtained and participants identified who are willing to come to the NIH Clinical Center for an MRAngiograph and venipuncture. DNA will be isolated and linkage studies undertaken to identify loci involved in the etiology of familial cerebral aneurysms, using standard linkage approaches.